Bart's troublemaking claims the life of a bird, and in repentance, he decides to take care of the eggs in its nest -- until he learns that the abandoned baby birds are actually reptilian pests who feed off birds.
-->'''Nelson:''' You even compensated for the crooked sight!
** Bart, after Marge punishes him by neglecting him and Bart realizes that he made orphans out of the eggs in the nest, decides to take care of them in repentance.
** Just in case you thought Marge was a little too hard on Bart for pretty much disowning him earlier, she helps him warm the eggs and even allows him and the lizards to escape from getting killed.
* BreadEggsMilkSquick: When the eggs finally hatch.
-->'''Marge:''' I see a foot!
-->'''Lisa:''' I see an eye!
-->'''Bart:''' I see a neck!
-->'''Homer:''' [[WhamLine I see a horn!]]
-->'''Lisa:''' (''confused'') A horn?
-->(''the eggs hatch, revealing lizards'')
* ChewOutFakeOut: After Bart reveals that he began taking care of the dead bird's eggs, Marge looks a bit disapproving at first... but then [[SoProudOfYou she smiles and gives Bart a hug]].
* CruelMercy: A non-lethal variant. When Marge finds out Bart has killed the bird, he realizes he can't run from this and says he deserves to be punished. Then Marge ignores him and lets him continue to "kill things", even though Bart clearly isn't proud of what he did either.
* DisappointedInYou: Marge, after Bart kills the bird, and just ignores him. She forgives him after discovering the birds' eggs.
* HypocriticalHumor: When Lisa and Maggie cheat at skeeball to get tickets, Nelson calls them out for this and then steals tickets from a machine that dispenses them.
* IDidntMeanToKillHim: Bart tried to explain to Marge that killing the bird was an accident. She doesn't buy it.
* IHaveNoSon: Marge realizing that her constant punishments of Bart never sink in and coming to the conclusion that he can do whatever he wants has this sort of effect.
* KarmaHoudini: Lisa, Maggie and Nelson don't suffer any consequences for the cheating and the stealing they did to get tickets.
* AMillionIsAStatistic: PlayedForLaughs towards the end.
-->'''Lisa:''' I don't get it, Bart. You got all upset when you killed one bird, but now you've killed tens of thousands, and it doesn't bother you at all.
-->'''Bart:''' Hey, you're right ... [[IgnoredEpiphany I call the front seat!]]
-->'''Lisa:''' You had it on the way over!
* MamaBear: By the climax both Bart and Marge feel this way towards Bart's lizards. Bart because he raised them, and Marge because she knows how it feels to love a kid even when everyone else thinks they're a monster.
* NotSoDifferent: Bart tells Marge during the climax that while he knows everyone else thinks the lizards are monsters, he still loves them because he sees them as his children. Marge of course, assures him that she knows exactly how that feels and helps him protect them.
-->'''Bart:''' Everyone thinks they're monsters. But I raised them, and I love them! [[ObliviousToTheirOwnDescription I know that's hard to understand.]]\\
'''Marge:''' [[SugarWiki/HeartwarmingMoments Not as hard as you think.]]
* ParentsForADay: Bart, hence the title.
* RunningGag: Homer falling downstairs into the unlit basement.
* TheScapegoat: When Bart asks for a go with Nelson's gun, he says he'll be pleased to have Bart's fingerprints on it.
* SkewedPriorities: When Nelson get enough tickets to win an easy-bake oven or a BB gun, he replies with this gem:
-->'''Nelson:''' Hmm... hot food is tempting, but I can't say no to a weapon.
* SuckECheeses and NoodleIncident: According to the sign outside, the Family Fun Center was once seen on the FOX reality special, "When Disaster Strikes 4." Viewers aren't given more information on how and why the Family Fun Center was featured there.
* SummonBiggerFish: Done 4 times in a row. After Bart releases the lizards to prevent them from being killed, Skinner warns him he has no idea what he has unleashed... and later changes his tune because the lizards wiped out the pigeon population, which the town considered a plague.
-->'''Skinner:''' Well, I was wrong. The lizards are a godsend.
-->'''Lisa:''' But isn't that a bit short-sighted? What happens when we're overrun by lizards?
-->'''Skinner:''' No problem. We simply unleash wave after wave of Chinese needle snakes. They'll wipe out the lizards.
-->'''Lisa:''' But aren't the snakes even worse?
-->'''Skinner:''' Yes, but we're prepared for that. We've lined up a fabulous type of gorilla that thrives on snake meat.
-->'''Lisa:''' But then we're stuck with gorillas!
-->'''Skinner:''' No, that's the beautiful part. When wintertime rolls around, the gorillas simply freeze to death.
* ThisIsUnforgivable: Marge's reaction upon learning Bart shot the bird.
* WhamLine: When the eggs are hatching, we get this from Homer...
-->'''Homer:''' I see a horn!
* WingPull: Just when Chirpy Boy and Bart Jr. look like they're going to be sent hurdling off a building, it turns out they have gliding membranes like [[https://en.wikipedia.org/wiki/Draco_volans flying dragon lizards]], which allow them to parachute down unharmed.
* YourApprovalFillsMeWithShame: Nelson inflicts this on Bart.